1. Field of the Invention
This invention relates to a device for collecting chemicals for analysis.
More particularly, this invention relates to a device for sampling and stripping volatile chemicals from ground water.
In a further and more specific aspect, the instant invention concerns a sampling unit for placement in a well casing to allow in-situ, real time analysis of volatile compounds in ground water.
2. Description of the Prior Art
Various devices are known for sampling ground water. One such device, which was disclosed in U.S. Pat. No. 4,717,473 to Burge et al., comprises a sorption column mounted underneath a pumping unit, whereby the pumping unit draws ground water through the sorption unit to allow analysis of various chemical parameters in the water. A special packer is provided for mounting the pumping unit and sorption column in a well casing and for preventing exchange of gases between the atmosphere and the ground water.
The above-mentioned device represents a substantial improvement over prior art samplers, since the packer eliminates numerous sources of errors usually associated with ground water sampling. For instance, it prevents foreign matter from dropping into the well. In addition, it prevents atmospheric oxygen from increasing the dissolved oxygen content of the water, which may result in the oxidation and/or reduction of several chemical species encountered in ground waters. Most importantly, it prevents the volatization of organic compounds, and allows for the collection of a time-averaged sample which is representative of the true contamination of the aquifer.
Nevertheless, the device disclosed in the '473 patent suffers from a number of shortcomings which make real-time analysis of samples impractical. For instance, the device fails to take into account the fact that most analytical methods require volatile compounds in a matrix of inert gas rather than water. Thus, any sample collected on the sorption column would still have to be transported to a location outside the well, where it would then be stripped of its volatile compounds and analyzed using conventional methods. At least some of these compounds will have been lost during transport, thereby reducing the precision and reproducibility of any test results. In addition, the device does not provide any means for calibrating analytical instruments within the well.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a device for allowing in-situ, real-time analysis of ground water in a well.
Another object of the invention is the provision of a sampling device having means for removing volatile compounds from ground water while the water is still within the well casing.
And another object of the invention is to provide a method of calibrating analytical instruments within the casing of a well.
And still a further object of the invention is the provision of a method and apparatus, according to the foregoing, which allow simple and accurate ground-water analysis at a relatively low cost.